This invention relates to a method and apparatus for scanning a movable record medium in a signal recording/playback device and playing and/or rerecording any signal information detected on the movable record medium. More particularly, this invention relates to a method and apparatus for scanning an audio tape in a logging system for audio content and replaying and/or rerecording any audio messages detected during the scan.
Scanning an audio tape either to avoid listening to long periods of silence or simply to move to another audio selection is a familiar process to one having ordinary skill in the audio recording art. For example, a common feature on stereo cassette tape players enables the user to move to the next selection on the cassette by pushing a forward or reverse "music scan" button. When such a button is depressed, the tape automatically advances to the end of the next blank section of the tape which separates selections.
In a multichannel logging system, this simple "scan past silence" technique does not function satisfactorily. A typical multichannel logging system is adapted to record any and all telephone communications which a large office, or, more commonly, a police or fire department, might receive during the course of a day or even longer period. Such logging systems almost invariably record the time such calls were received, using various methods to encode the time on a low frequency carrier signal for recording on the record medium (e.g. magnetic tape). Also, such logging systems frequently place a "guard" tone on all channels. This is done to verify that each channel is functioning properly. This "guard" tone is also generally a low frequency signal. If a "scan past silence" technique were used to scan for messages on a tape containing such time and "guard" signals, these signals would be detected causing the tape to stop when no message is actually present. Although the installation of a high pass filter with a low frequency cutoff above the "guard" and time code signal might suggest itself as a possible solution to the false triggering problem, such a filter would not correct the problem. When a tape is scanned for audio, it moves at some varying multiple of its normal playing speed. In a logging system, this speed may vary, for example, from 50 times to 100 times the normal playing speed of the tape as the tape is scanned. At these high speeds the various carrier signals shift upwards in frequency. For example, the time code signal may be shifted in frequency from 80 Hz to up to 8 KHz. A filter with a fixed cut off frequency would not be capable of removing both the time code and "guard" signals.